Surgeons have for many years used laser energy as a preferred means of light energy to achieve a variety of surgical effects. Among other effects, such energy can cut, vaporize, ablate or coagulate tissue. Based on various parameters, it is possible to irradiate diseased tissue, and cause its coagulation and necrosis, without injuring in a significant degree adjacent tissue that is healthy. It is known in hyperthermia, for example, that carcinogenic tissue, being weaker than healthy tissue, will necrose when exposed to temperatures from ca. 42 to 45 degrees Celsius, whereas healthy tissue, in general, will begin to necrose when heated to ca. 60 degrees Celsius.
When used interstitially, a probe is inserted into the tissue to be treated. In some interstitial cases, the surgeon desires to irradiate a generally spheroidal pattern about the fore end of the probe, and desires that the irradiation should be of dispersed, uniform intensity and thus progressively yield a controlled zone of necrotic destruction. The emission of light at the fore end of the probe is therefore both radial, or sideward, and axial, or forward. In other cases, as for example in order to achieve a cylindrical or ellipsoidal pattern of tissue destruction about the probe, only radial or sideward emission is desirable, and axial or forward emission is not. Typically, it is preferred that the radial emission should be dispersed over a predetermined surface area of the probe and at a generally uniform intensity. More and more, such probes are used percutaneously, and it is then desirable to use a tracking means to determine their location. It is then desirable to make the probe conspicuously visible using such a tracking device.
When operating intraluminally, as for example in atherosclerotic vessels, a surgeon may desire irradiation patterns similar to those in interstitial use. In some cases, the surgeon may even use a probe that can, to a limited degree, irradiate tissue that lies aft of the probe.
Generally, laser light that is conducted from a source of laser energy through a fiber-optic cable will not be emitted when it encounters the boundary of the light-conductive core of the fiber-optic material. The boundary is a smooth interface between the core of the fiber and a cladding about the core. The indexes of refraction of the cladding and core are selected such that the light is kept inside the core by total internal reflection until it is conducted to the distal end of the fiber-optic. Moreover, the light that may be emitted from the distal end of the fiber-optic cable will typically manifest a Gaussian intensity distribution: a preponderance of the emitted light is directed parallel, or nearly parallel, to the direction of the longitudinal axis of the fiber-optic cable.
Surgical probes that control dispersive radial and axial emission find use in photodynamic therapy, especially at low powers on the order of milliwatts. Probes similar to but more durable than the ones used in photodynamic therapy (PDT) find use in hyperthermia, in which powers of an order of magnitude of watts are usual, and a power of 30 watts is not unusual. It is also possible to enhance the effect of photodynamic therapy by concurrent use of hyperthermia. A probe suitable for hyperthermic treatment, however, must be able to withstand the temperatures that are produced for the therapy.
In order to produce a useful output for these and other purposes, it is necessary to alter the direction of the laser light from an axial to a radial direction and to ensure that the intensity of the emitted beam is smooth and uniform, with an absence of “hot spots”.
U.S. Pat. No. 4,592,353 to Daikuzono discloses a laser probe that can be used in direct, interstitial contact with tissue. The laser energy is coupled into the probe, which has no cladding. A coolant is applied to the junction, or gap, between the probe and the fiber-optic cable. Such probes have been used for interstitial coagulation and necrosis of tumors. Such procedures draw on principles of hyperthermia for tumor destruction. This probe, however, emits light from the end of the probe, using a lens to disperse the light in a cone with a whole angle of no more than 45E.
U.S. Pat. No. 5,380,318, also to Daikuzono, discloses a contact probe that disperses the emitted light in directions other than forward along the longitudinal axis of the fiber-optic. In one embodiment the probe is conical, and the external surface of the probe is roughened or is coated with irregularly-shaped transparent particles that will scatter the light. In another embodiment, the probe is a hollow tube or cap, and the inner surface of the cap is roughened or frosted. While these probes are more effective than the probes in Daikuzono '353 in diverting the laser energy from an axial direction to a radial one, they still emit a substantial proportion of the laser energy axially forward from the tip of the probe. These devices also show a significant peak in radiation intensity level with the tip of the probe.
U.S. Pat. No. 5,520,681 to Fuller et al. discloses a probe that disperses light by means of porosity or other inclusions within the probe. While these probes disperse the laser energy, they also generate heat, which may be harnessed for therapeutic use. Absorbent inclusions may be used to increase heating.
U.S. Pat. No. 5,054,867 to Wagnieres et al. discloses an apparatus for irradiating the bronchi of a patient for use in photodynamic therapy. A fiber-optic is surrounded by a first tube of polytetrafluoroethylene (PTFE); a brass cylinder holds the fiber-optic and tube in fixed axial position. Silicone, interspersed with titanium dioxide, fills the tube, but for a small air gap next to the brass cylinder. At the distal end of the first tube is set an aluminum cylinder, the proximal face of which acts as a mirror to light that is incident upon it. The aluminum cylinder is held in place by means of a second tube of PTFE which surrounds the first tube, leaving a small annular air gap between itself and the first tube, and extending beyond the end of the first tube. A PTFE plug is inserted at the distal end of the second tube, thus helping to hold the aluminum cylinder in place. The titanium dioxide is interspersed more heavily at the ends of the silicone-filled tube, near to the distal end of the fiber-optic and to the mirror face of the aluminum cylinder, causing the central region of the inner tube to emit less of the laser radiation than its distal and proximal regions. A trough-shaped reflective coating may be provided on the inside of the outer tube, to produce irradiation over only part of the circumference of the probe. This probe, having a metal reflector, will be limited in the powers that can be applied, for at high powers, the aluminum mirror face will absorb laser energy and may lead to destructive overheating.
U.S. Pat. No. 5,908,415 to Sinofsky discloses a transparent, plastic tube which surrounds and extends beyond the distal end of a fiber-optic cable. A silicone matrix, with light-scattering particles uniformly distributed therein, fills the tube. At the distal end of the tube is a reflective surface, and a plug caps the tube off. The light traveling from the fiberoptic cable to the distal end of the tube is complemented by the light that is reflected back from the reflective surface, to produce a comparatively uniform light intensity along the length of the tube. The distance between the distal end of the fiber optic and the reflective surface, and the concentration of the scattering particles, are selected to create an intensity distribution pattern that does not vary more than plus or minus 20% along the length of the tube. No air bubbles should be within the matrix. While on the one hand this fiber-optic device produces a relatively uniform radial emission and while it is relatively easy to manufacture inasmuch as it has a uniform concentration of scattering particles, on the other hand the probe depends overmuch on the back reflection from the distal end of the device in order to achieve uniformity. The load that is put on the metal reflector can lead to overheating.
U.S. Pat. No. 5,431,647 to Purcell et al. describes a fiber-optic cable the core of which is stripped of its cladding over a distal length. Over that stripped length is snugly fitted a transparent sleeve in which light-scattering particles have been embedded. The sleeve acts as an extension of the core, so that light enters the sleeve and is scattered out sideways. Abutting the distal end of the fiber-optic is a metallic mirror to reflect back the light that has not been scattered and emitted through the sleeve. The mirror is held in place by a transparent cylindrical cap which also surrounds the sleeve and which affixes to an outer buffer of the fiber-optic cable. An air gap is maintained between the cap and the sleeve, and acts like a cladding to the fiber and sleeve. Intensity distributions varying no more than plus or minus 30% are reported to be easily obtained. In this probe, however, little is done to randomize the laser energy before it reaches the distal metallic mirror, and for this reason, if high powers are used, the mirror will overheat.
U.S. Pat. No. 5,269,777 to Doiron et al. describes a fiber-optic from which the jacket has been stripped at the distal end. Abutting and extending fore of the fiber-optic is a first silicone portion. Surrounding the first silicone portion is a silicone sleeve, in which are embedded light scattering particles. The concentration of the particles may be varied to achieve uniform or otherwise specified output patterns. Within the first silicone portion can be distributed light scattering particles, whether in discrete blocks or in continuously graded or melded concentrations. A sheath surrounds the silicone sleeve and a portion of the jacket that has not been stripped from the fiber-optic cable to provide the necessary rigidity to the tip assembly. It is asserted that the output pattern is substantially independent of the divergence of the laser beam that is coupled into the fiber-optic. This probe has little in its design to prevent the forward emission of the laser energy. In practice, either it will be limited to low powers or to applications where forward emission is immaterial or desired, or else the forward emission will be reduced by a concentration of dispersant that causes a non-uniform radial emission pattern.
U.S. Pat. No. 4,660,925 to McCaughan describes a fiber-optic cable that has been stripped of its buffer and cladding at the fore end. The distal end of the fiber-optic is carefully cleaved and polished. Layers of a scattering medium are applied to the exposed portion of the fiber-optic. Each layer is inspected and polished manually to ensure a spherically uniform emission of light, with concentrations of scatterers increasing logarithmically to the fore end, thus ensuring a uniform cylindrical distribution. A tube is tightly fitted over the painted portion of the fiber-optic. No air or contaminants must enter between the tube and painted portion. Little is done in this probe to randomize the laser energy traversing the fiber-optic, and the titration of the scattering medium according to a logarithmic pattern is not easily achieved. As a result, this probe will not find application at high powers.
U.S. Pat. No. 5,947,959 to Sinofsky discloses a device in which a transparent tube is affixed to the distal end of a fiber-optic cable. The tube surrounds and extends beyond the optical fiber. The tube comprises a single chamber which is filled with a diffusive medium which incorporates light-scattering particles of a uniform concentration and which is characterized by a single dielectric constant. A metal plug, typically gold, is set at the distal end of the tube, and serves primarily to allow image-guided location of the distal end of the tube. Light that reaches the metal plug can cause it to heat, and such heat may damage the tube or surrounding tissue. A dielectric reflector consisting of a stack of layers of different, alternating dielectric constants formed on a glass substrate and is placed aft of the metal plug. The dielectric constant of the first layer is preferably greater than the dielectric constant of the diffusive medium. The interfaces between the layers reflect a high proportion of the light backward into the tube, while generating minimal heat at the interfaces. The interfaces are spaced to produce constructive interference of the backward reflected light, assuming that the light is traveling axially. Where the dielectric reflector is used with a metal reflector, the metal ensures that forward emission out of the distal end of the tube is nil to negligible, though some of the light will be absorbed by the reflector and be converted to heat. Where the dielectric reflector is used without a metal reflector, it is assumed that the amount of light that is emitted forward is insignificant and will not injure tissue or damage other instruments. However, the laser energy reaching the dielectric reflector will have been at least partly scattered and therefore there will be a wide range of incidence angles at the interfaces. Light incident at wide angles will not benefit from constructive interference, so the dielectric reflector will undesirably permit the wider-angled energy to propagate through.
Each of the above devices found in the prior art seeks to divert some or all of a laser beam from an axial direction and emission to a radial direction and emission. However, none is practical in dealing with powers that could lead to forward emission that could undesirably injure tissue fore of the device or with powers that could undesirably overheat a reflector at the distal end and thus destroy the device.
What is needed is a device which effectively randomizes the path of the laser energy as it is propagated through the radially emissive portion of the device and achieves substantially uniform radial emission (or other controlled emission patterns), but which even at high powers generates immaterial heat at the device and can control the level of forward emission to a therapeutically exiguous amount.